Welding is the metallurgical joining of separate metallic workpieces. Typically, during welding, two workpieces are brought into proximity to one another. A portion of each workpiece is melted by localized application of heat with a torch connected to an electric welding power supply apparatus to form a pool of molten metal between the workpieces. Heating the workpiece is often accomplished with a welding torch, such as, a Metal Inert Gas (MIG) torch or a Tungsten Inert Gas (TIG) torch. As is known, MIG welding may be referred to as Gas Metal Arc Welding (G MAW) and TIG welding may be referred to as Gas Tungsten Arc Welding (GTAW). Other types of welding may include gas welding, and Flux-Cored Arc Welding (FCAW). In each of these welding processes, a filler material is often added to the pool of molten metal, also known as a weld pool. The filler material may be in the form of a metallic stick or metallic wire.
Once formed, the weld pool is translated or moved along a predetermined path between the two workpieces. The filler material is continuously fed into the weld pool at a controlled rate as the weld pool is translated. The metal in front of the weld pool is melted while the mixture of metal and filler material in the wake of the moving weld pool solidifies as it cools. A weld joint between the two workpieces is formed once the weld pool of molten metal cools.
While welding may be manually performed with a weld torch, it is an automated welding system for large volume manufacturing operations. These systems often include a robot or other electro-mechanically articulated machine to move the welding torch relative to the workpiece. By programming the robot, it may repeatedly trace the torch across the workpiece in a precise, preselected path or along a path that is corrected by external sensors. The filler material in wire form may be fed from a wire spool by an automatic feeder carried on the robot or in close proximity to the robot.
Many of the above-identified welding processes require a shielding gas (e.g., a nonreactive gas, such as, argon). For example, MIG welding requires the use of an inert shielding gas to surround the electrode and the weld pool. The shielding gas displaces normal atmospheric gases from around the molten metal. Shielding gas thus forms a localized gas barrier or buffer between the molten metal and normal atmospheric gases. By providing this barrier, the shielding gas prevents undesirable gases in the atmosphere from reacting with the molten metal. It is known that molten or hot metal may react with atmospheric gases, for example, nitrogen and/or oxygen, and can result in poor quality weld joints. For example, weld joints containing undesirable reaction products, for example, porosity and/or metal oxide inclusions, may exhibit unacceptable properties, such as, poor mechanical strength and poor corrosion resistance. Use of a shielding gas thus generally improves weld quality.
For those welding systems that require a shielding gas, a control system for delivering the gas to the torch may be used. The gas control system may include various regulators and piping to regulate the pressure of the shielding gas and to control its delivery proximate the weld pool. Normally, the delivery is manually controlled with a flow meter, which may be downstream from a pressure gauge coupled to a gas cylinder or bulk gas supply source. Consistent delivery of the minimum required shielding gas is problematic.
Problems with delivery may cause problems with the quality of the weld joint due to variations in the gas barrier. The gas barrier around the weld pool may vary for any number of reasons, for example, simply by virtue of the distance from the supply of shielding gas. Simple procedures may be used to deal with variations in shielding gas flow over the weld pool and the problems associated with insufficient shielding gas.
One common approach is to use an excessive amount of shielding gas by manually setting the flow control to a high level during the entire welding process. Once set, the manual setting is not later adjusted during the welding process. With this approach, even though there may be variation in gas flow, at least the minimal amount of shielding gas will always be present.
In view of problems with existing welding systems, and while welding systems have generally been successful, manufacturers of welding systems and their customers continuously strive to improve their welding systems and welding processes, particularly weld quality and weld quality consistency, while reducing costs.